Posted
by
samzenpus
on Sunday July 01, 2012 @09:42PM
from the never-lost dept.

dangle writes "BAE Systems has developed a positioning solution that it claims will work even when GPS is unavailable. Its strategy is to use the collection of radio frequency signals from TV, radio and cellphone masts, even WiFi routers, to deduce a position. BAE's answer is dubbed Navigation via Signals of Opportunity (NAVSOP). It interrogates the airwaves for the ID and signal strength of local digital TV and radio signals, plus air traffic control radars, with finer grained adjustments coming from cellphone masts and WiFi routers. In any given area, the TV, radio, cellphone and radar signals tend to be at constant frequencies and power levels as they are are heavily regulated — so positions could be calculated from them. "The real beauty of NAVSOP is that the infrastructure required to make it work is already in place," says a BAE spokesman — and "software defined radio" microchips that run NAVSOP routines can easily be integrated into existing satnavs. The firm believes the technology could also work in urban concrete canyons where GPS signals cannot currently reach."

Personally, I think we need less technology to pinpoint where we are. Trading convenience for security and privacy and all that.....

As a privacy and security freak I disagree. The problem is not location accuracy. It is information leakage. There are all kinds of great things I can do with my own location info. The problem is all the devices that gleefully hand over my location info to 3rd parties who wish to exploit it for their own benefit.

Use a real GPS unit with no broadcast capabilities and you don't have that problem.

And you also won't have the benefit of having a computer able to access your location data either. Seriously, that's a non-answer. We easily have the ability to do the right thing. Giving up on doing anything sophisticated just because there are groups who want to abuse it too is basically the historical definition of luddism.

Use a real GPS unit with no broadcast capabilities and you don't have that problem.

And you also won't have the benefit of having a computer able to access your location data either.

Why? Since I've done it, and its common knowledge how to do it, I'm thinking thats just wrong. Hard to believe its been over a decade since I was experimenting with ham radio APRS using a GPS, simply unplug the transmitter/set the broadcast timer to zero (or a billion) and you're done. Ever since the first NMEA output jack on a GPS in the 90s, people have been hooking them up to laptops and fooling around with big screen navigation displays (like a giant aircraft HSI, but for boats), homemade boat autopilots, automatic fishing trawling autopilots, homemade moving maps, stuff like that. The GPSD daemon has been around for I believe 18 years now, so 18 years ago it changed from a curiosity/hack to a very standardized interface. GPSD is currently maintained by ESR, you may have heard of him over the decades.

The only reason "your" computer aka cell phone broadcasts your GPS position without any control by you is because you bought into a walled garden. Its not your phone, and its not working for you.

I think he's asking for something more like a Garmin 72H which has a screen with navigation and a NMEA output. There's probably a cheaper one out there... You're looking at $100 or so, guess it depends on how you define "reasonable price".

This is very much like the cell phone/ipod touch situation where its dramatically cheaper to buy each separate, but if you insist on both in one case you'll have to pay a lot of extra money.

No, I understood you, thanks. But you're asking for two things that (you've noticed!) don't line up, so if you want to have your cake and eat it too, you can take my advice and not be a dick about it. Or not, I don't really care, but it sounded like you had a problem and were more interested in a solution than pedantry.

Consumer-level satnavs aren't intended, built, or particularly suitable for connecting to a computer. A cheap dedicated Garmin GPS unit (as opposed to satnav) will do just fine in terms of lo

Why? Since I've done it, and its common knowledge how to do it, I'm thinking thats just wrong.

Same reason the DMCA prohibits the distribution, but not creation or use, of DRM circumvention tools. You can certainly jerry-rig something, but wide-spread adoption of it is exceptionally unlikely. When only the technical elite are capable of putting something together than its value to humanity is basically nil.

All true. Right now the only "safe" GPS devices are those which have no capability of being connected to anything. It doesn't have to be that way. In-car navigation systems could be designed to not reveal your location to anybody except you. They could have a button on the dash that says "transmit my location" if you want to use the services of a central office. The car could only transmit that data itself in case of an accident, assuming of course you gave it permission in advance to do that. You could have a phone or computer app that would tell YOU where your car is instead of some central monitoring station, and YOU alone could have the ability to disable your vehicle, which would be appropriate since you'd be the only one who knows where it is.

Also, your smartphone could easily keep logs of "I told your location to X at these times during the day" and other such sensitive data like that. Everybody likes to use phone logs against people, why can't we use them FOR people for a change?

All of this is possible, but nobody seems to build it. I wonder why that is?

For now, remember that if your device can act intelligently on your location, it can and probably does do so for someone else's purposes too. If there is a microphone that you don't have a physical plug or off switch to, somebody besides you can turn it on and off. Your modern conveniences might provide some convenience for you, but they are VERY convenient for law enforcement on fishing expeditions, private investigators bribing system operators, etc.

My Galaxy Tab with OSMand did a pretty good job of tracking my location without me being connected to Wi-Fi. Of course as soon as I got home and connected, Facebook and Google probably learned everywhere I'd been that day.

This can only work if you have a DB of precise locations of wireless signals. Even assuming that is viable, it cannot replace GPS as is.

Whenever a program is looking-up the location of a smartphone, that phone is very probably also beaming back a list of all the Wifi APs in-range, their signal strength, and approximate location. Everyone who makes navigation software for smartphones is guaranteed to have such a database, and is continually keeping it up-to-date.

Not only is it practical to do this, and it has been for years and years, it's done because you're likely to get much better accuracy, and a much quicker location fix. You can prove this out by running a navigation app on a tablet that has wifi but lacks a GPS chip. You'll find that Google Maps or anything else has no problem at all pinpointing your location.

And BTW, moving one AP won't cause a problem... Triangulation requires several APs in range, and it'll try to use everything in-range to get a more precise fix so... Short of conspiring to have everyone in an area to move their APs in unison for a significant distance, you're not going to significantly fool the algorithm that handles all of this.

What's more... Before wifi was widespread, the previous fallback was a database with the GPS coordinates, altitudes, power levels, etc., of all of a telco's cell towers. It works, but not as well as the horde of prolific wifi APs these days. And for the record, I am speaking from first-hand knowledge.

Sure, pinpointing your location to a street corner isn't that hard, but consumer level GPS receivers can pinpoint you to within about 3 feet in most conditions. I doubt you can do that with signal strength measurements.

Sure, pinpointing your location to a street corner isn't that hard, but consumer level GPS receivers can pinpoint you to within about 3 feet in most conditions. I doubt you can do that with signal strength measurements.

Anyone with access to Apple's WWDC videos should watch the video about improved mapping, which demonstrates nicely how in some parts of San Francisco GPS on its own is practically worthless. From experience, there are areas in London where it's the same.

Cincinnait, OH is a real joy to navigate via GPS as well. Unfortunately for this scheme, cell and broadcast reception is often flaky. I think pretty much any city built on hills is going to be ASS HAAT. (seewhatididthere)

If there are enough signals around you and you have enough users (who report all signals they see, so as to get their location), you can always update your database on the go (just like Google does right now).

Yes. Gather an initial DB and have it "self heal" as wireless signals change.

This is precisely what Google are doing with the combination of an initial street view drive followed by an army of android phones to keep the DB up-to-date. While every android phone continues to help update the database there is a good chance it will be very accurate.

I think it's a great idea, but not very novel. Google, Apple, Microsoft have implemented this and been using it for a long time.

Collecting SSIDs and correlating to locations is completely legal.
What happened was that the cars were also (accidentally?) collecting unencrypted wifi data at the same time (and in my opinion, while this was a mistake, what expectation of privacy should you have when you don't spend the 5 seconds it takes to tick 'WPA'?)

GPS has everything to do with privacy, as it is currently implemented.

Where is a standalone GPS? Pretty damn few out there right now.

The challenge with GPS is that nearly every consumer device out there we are shoving it into does not let the consumer control who gets the information. You may *think* you control it, but you really do not. Too many things ask for it, even though it is not required, and the carriers get it anyways.

You don't have to be wearing tin foil to have legitimate concerns about tech

Are your eyes closed? Every electronics store is full of them. Walmart, BestBuy, Radio Shack, Target, every store you can think of sells nav devices.

Contrary to slashdot's ignorant belief, not every person on the planet does everything on their android device. Some of us realize some devices are actually suited for their tasks rather than trying to be a one size fits all solution.

Probably uses carrier-phase correlation. When a good GPS fix is available, it can capture the carrier phases of the available 3rd-party signals, then when the GPS fix is lost, it can recover the position through correlation.

Its not using signal strength. Its using position. You have a set of internal antennas, that are tenths of a degree apart arrayed in a circle. You get a strongest signal from the set of elements that are orthogonal (at right angles in 3 dimensions) to the source. You can calculate based on signal strengths of two 'strongest' sets of elements the direction (accurate to perhaps 1 second of arc), the direction to one source. Then you switch frequencies and determine the location to a second source (again,

You have a set of internal antennas, that are tenths of a degree apart arrayed in a circle. You get a strongest signal from the set of elements that are orthogonal (at right angles in 3 dimensions) to the source. You can calculate based on signal strengths of two 'strongest' sets of elements the direction (accurate to perhaps 1 second of arc), the direction to one source. Then you switch frequencies and determine the location to a second source (again, accurate to 1 second of arc).

From a EE/optical perspective this doesn't work. Its the same equations for lens and antennas. For a wavelength around 2.4 GHz calculate the antenna/lens size required to resolve to an arcsecond and get back to me on how to install hundreds of them inside a handheld device.

What would/could work, although not as well as you may desire, is an interferometer design, although thats also gonna have serious issues and you're not going to achieve one arcsecond resolution.

Bullshit at least to the extent that this is suppose to "rival" GPS.Isn't GPS good to something like 3m out of the box?From the no details that's been given, they'd be lucky to get 300m (hardly a "rival" if you are 100x less precise).99%+ of all arbitrary "signal of opportunity" cannot yield precise distance information.They would almost certainly want to use some kind of directional antenna. Again, hardly a "rival" if you need a vehicle to mount your contraption, and it's 100x heavier.

My ye olde Blackberry Curve 8300 predated widespread GPS in phones, but was still able to fix my position in cities within 300ft or so (good enough to get "directions from my location to ____") based on signal strength from nearby towers. This is a known technology. Granted, position on the highway is terrible (usually within 2 miles on the interstate out in the country) but as long as your mapping program can figure out which interstate you're on, it can generally give useful directions. Augmented

Ever tried to use a GPS in New York City? I'm guessing that comparing hundreds of signals would tend to be more accurate and more stable than GPS in that environment even if the precision of the fix isn't as good.

This is essentially the system used by the original iPhone, before it had proper GPS. Using data from Skyhook Wireless about the location of wifi APs (identified by MAC), combined with the data from its phone transceiver about "visible" cell towers, it inferred the phone's position. It works, but (as shown by the fact that Apple added true GPS in the iPhone 3G) not as accurately as GPS. (I think the iPod Touch still gets by using just the wifi data, which makes it susceptible to confusion if someone with

Article was not very clear on how the "radiomaps" are updated to NAVSOP devices. Assuming you can use SDR radios to triangulate your position, you still need to have a database of known stations / frequencies / locations. Given that there are probably over 300M Wifi accesspoints, plus probably millions of radio/TV/other stations on the planet how does this system generate and distribute this kind of "radiomap" database?

A stereotypical semi-advanced microcontroller/DSP lab exercise is building a VOR display like from an aircraft. The protocol for a VOR is simple, I don't remember exactly, but a continuously transmitting narrow beam antenna rotates continuously and transmits a 1000 hz signal and every time it flings past geographic north it transmits a precisely defined pulse of a couple cycles of 2500 hz. Or whatever. It rotates pretty freaking fast like once per second. The point being the algorithm is you play DSP ga

A-GPS still uses only GPS signals for positioning, but gets help from a data network (not necessarily mobile). Basically it receives certain orbital info of GPS satellites that are normally transmitted on the GPS signal itself. But regular GPS data is slow, it can take ten minutes or more to get all data complete. Over the network it's a fraction of a second. This often helps getting a fix much faster than with plain GPS, but the location itself is pure GPS based.

Some phones may also use the mobile network for triangulation, independent from GPS, and usually less accurate.

It takes more than 10 minutes to receive the entire almanac but for operation only the ephemeris for the received satellites is necessary which takes up to 30 seconds. It takes longer for PDAs and phones A-GPS because of the abysmal performance of their GPS receivers.

It takes longer for PDAs and phones A-GPS because of the abysmal performance of their GPS receivers.

You say that in a pretty negative tone. I know the first iPhone created such an image (and its GPS was poor), but it's far from true these days.

My cheap-end smartphone, with A-GPS, often has a fix within seconds. Without A-GPS it surely takes longer. Accuracy overall is good. Phone GPS performance is very similar to that of dedicated GPS devices of about three years ago.

It sounds like they're able to provide a fix without GPS, which would give it an entirely different function from AGPS.

AGPS tells a GPS receiver where satellites are supposed to be at a certain time, to help it initially lock on to their signal. It does not provide a higher-precision location, or one at all in places where GPS cannot penetrate.

AGPS tells a GPS receiver where satellites are supposed to be at a certain time, to help it initially lock on to their signal. It does not provide a higher-precision location, or one at all in places where GPS cannot penetrate.

It depends on your definition of AGPS really. In the real world, systems like iOS, skyhook, (and probably Android, not sure) do exactly what this article describes already - they use signals like cell phone masts and Wifi SSDs to work out where they are, as a separate and independent step to GPS location (though they may then use that rough location to assist GPS locating). They call this AGPS, but you can call it whatever you want. If you turn off the GPS in your iPhone, or use a wifi only iPod it will sti

While this was originally true, it's not any more. The Assisted Global Positioning System in the modern cellular network is so accurate, it can fairly reliably replace baseline GPS inside buildings in urban areas and it has been doing so for devices that support it long ago (for example, my ancient nokia 5230 which I use for navigation has this ability).

Quoth wikipedia:The Wide Area Augmentation System (WAAS) is an air navigation aid developed by the Federal Aviation Administration to augment the Global Positioning System (GPS), with the goal of improving its accuracy, integrity, and availability. Essentially, WAAS is intended to enable aircraft to rely on GPS for all phases of flight, including

For a somewhat more recent example, A-GPS is more or less DGPS but over the internet instead of over a radio beacon. Yes this is yet another one of those tiresome "something people have always done... now over the internet!" patents.

I briefly considered becoming a surveyor around the time DGPS was "new". It was expected to replace the microwave based ranging finding systems. I have not kept up to find out how that all turned out. My impression of surveyor training was I

Sure in an open area the signal strength from broadcast and third-party location services is fine but so is GPS.

But in an urban environment these are not accurate signal strength is only loosely proportional to inverse square of the distance so any accuracy will utterly break down. I can't see them having the money investing on getting a location DB for coverage outside major cities meaning you have to ship an unusable feature to most of the population.

The firm believes the technology could also work in urban concrete canyons where GPS signals cannot currently reach.

This will only work by regularly updating a database of local signals by driving down these roads and walking around areas. You might get the reliability for a consumer device but SDR like this can hardly be cheap, small and low power.

Possibly they have algorithm to make this manageable but i would think installing purpose built transmitting devices at every street corner would be a better option.

Signal strength is unreliable, as it depends on the atmosphere in between you and the transmitter. Yet you may be able to get time data (summary mentions digital signals only) and based on that calculate your distance.

In urban, in my experience, GPS signals can generally be received but are unreliable due to reflections: the GPSr assumes direct line to the satellite, not via a reflection. As a result GPS in urban areas is often off-set, or jumpy (location jumps by 20-30m in any direction)

Signal strength is unreliable, as it depends on the atmosphere in between you and the transmitter. Yet you may be able to get time data (summary mentions digital signals only) and based on that calculate your distance.

I think its very possible to achieve this as long as the signals you rely on are line of sight. They will have smart people working on the problem.They use digital signals as most analogue signals have large wavelengths that cannot be picked up by cell phone size antennas and they also may have broadcast IDs.The article makes this look like a solution to a Military problem where they can maintain intelligence on broadcast sources that will be line of sight, when the enemy brakes GPS.

In urban, in my experience, GPS signals can generally be received but are unreliable due to reflections: the GPSr assumes direct line to the satellite, not via a reflection. As a result GPS in urban areas is often off-set, or jumpy (location jumps by 20-30m in any direction)

I think it benefits the conversation to be specific between "Localization" and Simultaneous Localization and Mapping (SLAM). The first one gets easier to do as the quality of your map data improves. The wonderful thing about being alive today is cellular carriers are strapping extremely sophisticated & sensor packed data-acquisition modules to almost every person roaming this planet. These smart phones get retired on a semi-regular basis, and as a result the logistics of adding a new sensor to the famil

They could have an app or query my phone. It'd reply with my GPS position and that the signal strength to 4 towers by name/ID. Enough tags like that, they can identify the towers in 3D space and go from there.

Enough tags like that and location can be found just from tower information.

For the general public this is for when GPS does not work. The product will require extra hardware and if they want the best results a lot of extra hardware in there mobile device. Cellphone antennas are optimized for cellphone frequencies they are not designed to pickup frequencies so it may require extra antennas on the device. This is far more complex in the real word than GPS, you would only use this where GPS does not work.

I was thinking they could detect and report unexpected changes to wireless sign

But in an urban environment these are not accurate signal strength is only loosely proportional to inverse square of the distance so any accuracy will utterly break down.

There's a bit more to it than that.

First: Inverse square falls off FAST near the transmitter. For distant transmitters, like TV stations and (rural) cellphone towers, you have the problem you describe. But for WiFi in nearby houses or other apartments in your own you can get a pretty good idea where you are just from strength.

I now realize that the target is car mounted units that use to rely on GPS which i think is far easier. Smart phones have more things that are unknown with battery and space constraints.

TV stations (especially since the changeover to digital and the use of multiple synchronized transmitters sending the same signal on the same frequency) and cell towers all send fantastically accurate timing references.

This might get you the right street or block almost all of the time but there will still be times it can't do or gets it wrong. Path distance is hardly reliable in an urban environment for initially locating your position. Filtering the estimated position over a trip probably they probably have worked out, especially if they

I see it working in a car mounted GPS device, though it sounds like extra external sensors and large amounts of storage are required to achieve the stated accuracy along with partial GPS coverage.

But indoor or urban mapping from a smartphone does not look like its solved. Indoor mapping using only censors available to a smartphone is not the same as this works while my phone is in my pocket where my hand, briefcase or anything else is swinging past it while I am moving though doors. In areas where you can't

While it sounds like this would work decently well in cities, it probably won't have nearly as many signals to work with in less populated areas, and it would be practically useless out in, say, the middle of the Pacific. So at best, it's a complement to GPS, not a replacement.

Second, how is it going to match up different sources with physical locations? I assume they'll just have a massive database of "this wifi router is located at 31.41592N 27.18281W, this AM transmitter is at....", but that brings up even more problems. Who will maintain that database - the big regulated transmitters can probably be figured out easily, but WiFi routers? How much space will that DB take up - could make it prohibitive on some devices?

The database is stored centrally. You provide information on which towers / wifi devices you can see with their signal strength. And the central database either works out your location for you, or returns the known location of each of the devices you can hear. And it will probably use the information you supply to improve the quality of the database.

It interrogates the airwaves for the ID and signal strength of local digital TV and radio signals,

So let me drive 3 hours north of Perth, Western Australia [google.com.au] and find that this system is as useful as an ashtray on a motorbike.

I cant really see a use for this technology that GPS doesn't already fill and a huge drawback because as soon as you get to places with only one mobile phone tower or one source of TV signals (most rural towns in Oz) its fucked (the fewer sources you have for triangulation, the less accurate the result). Then we have the great wide expanse between towns which can get up to 500 KM of open road with no TV, no mobile coverage, no WiFi networks and even AM radio is spotty at best. In fact in many places the only source of radio transmissions will be from 2 way radios mounted on trucks... if there happen to be any trucks in the area.

Really this is some nice research BAe but it has no practical use outside the lab. Seeing as it's only useful within cities any commercial product will remain inferior to traditional GPS.

They're not trying to replace GPS - it's to augment it when GPS doesnt work. If you have a receiver with both systems you are far more likely to have one of them work, because most of the obstructions for GPS also go hand in hand with the availability of other networks.

Sure it might not work in the middle of the outback, but GPS generally will so it's not the target market.

Given that it was produced by BAE Systems, a company noted largely for their defense contract work(and, since their acquisition of Marconi, this includes extensive defense electronics and RF stuff), I strongly suspect that the punchline of this work (while they probably won't say no to sufficiently lucrative commercial licensing offers) is having a product offering that provides some degree of reliability for location-dependent military hardware and munitions even if GPS is jammed, knocked out, disabled by

Short sighted much? The nice thing about places where there's not much RF transmitters is that there's usually bugger all in the way of people there who need to find their location. Not to mention there's also usually open sky so GPS works just fine.

It interrogates the airwaves for the ID and signal strength of local digital TV and radio signals,

So let me drive 3 hours north of Perth, Western Australia [google.com.au] and find that this system is as useful as an ashtray on a motorbike.

Now, why would you want to drive 3 hours north of Perth anyway, if there are no digital TV or radio signals there? There is no need for a navigation system to get you to a place no one wants to get to. As to finding your way to towns separated by 500KM of no TV, just follow the road. There is only one between the two. "You can't get lost, from here, to there!"

Of course, Australia already has an excellent built-in Navigation System infrastructure: Aborigines. They have been wandering the continent for

If your GPS signal is blocked by skyscrapers and bridges I'd really suggest you open your eyes rather than looking at the GPS. The areas you're refering to are so few and far between and so dense that you really should just put down the gadget for 10 minutes and walk the final block to your destination.

Because we all know how reliable & accurate cell tower triangulation is. That's why wireless phone's all have A-GPS being built-in, because the networks accuracy was at best a few blocks, which the FCC considered unacceptable for the nation's 911 systems. WiFi systems have such a long signal reach, many miles no doubt. Radio stations always broadcast as exectky the same power, which is why somedays you can hear them much better than others. I doubt that this will be long lived

One interesting challenge not mentioned in the description of BAE's system is how they create the map. GPS has relatively few satellites and they broadcast their positions which is used by a receiver to determine it's own position. Relying on other radio sources will mean having them all mapped. Either the receiver needs knowledge of all of these ( unlikely) or it gets updates for it's local area periodically over a data channel. The map is also likely to be more than just an antenna's location, but data as to how it's received based on local topography. Alternatively it could send a snapshot of what radio signals it receives and the position is actually determined back at a server and relayed back to it. Either way seems to presume a separate data connection to the receiver to either load the whole database of signals sources ( and update it ) or a continuous connection to get the local database as it goes.

Using other signals of opportunity would be a good way to augment GPS, but surely not a replacement. Not being a replacement, I'd have a hard time calling it a rival.

In a search and rescue situation I can imagine a team of people each with one of these devices, as well as GPS. If the devices can communicate with each other (as a mesh network) they could pinpoint location based on the different times they see the same signal. Furthermore, if the mesh eventually reaches a position where GPS is available, this signal could then be used to establish an anchor position.

Finally, and I don't know if this was covered, but presumably this system would also allow for vertical

More than a decade... I saw a working demonstration of a such a system in 1992 using the fixed locations of public radio masts as triangulation points. In densely populated areas, such as Cambridge, UK, the system could resolve location to within 50cm if I remember correctly.

About a decade ago I remember talk of radar via this same technique. AFAIK that never came to fruition.

Talk called bistatic radar or passive radar. Oh, its deployed and in use. The 1950s DEW line had something like this if you want to get all picky. The hilarious part about this whole discussion is the company behind this press release, BAE systems, has been selling a.mil version of passive radar called CELLDAR for about a decade that uses cellphone base stations. Its not a huge conceptual jump between passive radar and passive navigation.

I used to work for a subsidiary of TruePosition. One of the ventures they worked with developed this technology several years ago. It used the timing differences in the TV signals to ascertain position. TP acquired interest in that it provided the ability to obtain a location in areas where GPS sucks - like downtown Manhattan or other dense cities. Using external positioning devices, this technology could also provided high accuracy positioning within buildings - including altitude.

At Zoombak, we extended the positioning technology of our device to be able to use the signal strength and radiation patterns from the various cell towers to derive a lower accuracy location when GPS is not available (you need 4 visible satellites). And, WiFi can be used for even positioning by knowing the location of WiFi routers and map the RF signal.

I'm just thinking through this. If my phone's battery is charged, it's likely my GPS will still work in a large blackout that covers most of a metro area - navsats have their own independent power, of course.

But, in a large blackout, seems like most RF sources would probably go silent. Especially WiFi AP's (I suppose some people might have them on UPS's, but I suspect most people do not).

Radio Stations and TV's probably have emergency generators so they stay on the air in a blackout. Same for police/fire/em

1. It would require a very large and dynamic database, and that database would require updating almost every minute, as transmitters change "signatures", are switched on or off, or are interfered with by atmospheric phenomena. The storage and computational power required to do so would keep a midrange desktop machine busy almost 100% of the time.

2. Significant events that disrupt the power grid, such as the derecho [noaa.gov] in the eastern US over the weekend, would render

It's great to see this much interest in NAVigation via Signals of OPportunity. I can't reply to everyone individually and certainly can't get into huge discussions, I've scanned this thread and thought I could give you some information to help clear some of the mist.

1 - Radio positioning is certainly not new, people are discussing Rosum here, and (in a round about way) Cambridge Positioning Systems - the latter funded my PhD at Cambridge in this topic, and I've been driving developments in this field for the last 5 years. I'm not claiming to have invented multilateration or opportunistic positioning, what we have been doing at BAE is working on removing a lot of the restrictions discussed on here - for example getting rid of the need for access to a database someone else created of all the transmitter locations, or access to differential corrections from a reference receiver. A lot of the "this is not new" comments refer to differential positioning using reference receivers and having access to databases of transmitter locations (Rosum, the old Cursor positioning system from Cambridge Positioning Systems, etc). We consider those aspects to be undesirable constraints on a flexible opportunistic positioning system and don't rely on them. The system determines the transmitter locations itself, or gets by witout actually needing to locate the transmitters at all (for example our indoor positioning system does not aim to or need to locate the transmitters to function) We have developed some Simultaneous Localisation and Mapping algorithms (again not pretending to have invented the concept, just developing new algorithms building on these methods for use in opportunistic radio positioning) to aid the learning process and allow operations during GPS denial but before any transmitters have been fully calibrated via GPS, and we also exploit the fact that we are not limiting ourselves to jerry-rigging existing devices (e.g. cellphones) to do things they weren't designed for. We also look at some exotic concepts that are too computationally expensive or demanding in hardware to ever be applicable to the civilian sector, but are applicable to other sectors.

2 - We record as many metrics as we can - phase, phase rate, arrival of certain repetitve signal structure (time of arrival), signal strength, etc. We use different metrics in different environments - for example signal strength is more useful indoors to discriminate motion than outdoors. See my ION paper for more on the indoor system http://www.plansconference.org/abstract.cfm?meetingID=36&pid=51&t=C&s=1

3 - The entire concept is based around learning - the system gets better with use. When GPS is available you can start learning about the locations of the transmitters around you, their signal stabilities, start recording signal strength fingerprints, etc. Most (but not all) types of radio transmitter can be localised by our techniques. So imagine driving into a city along a motorway - you start to learn about the DAB transmitters, DVB, cellular etc available and start to localise them. Even without fully determining their location you quickly determine what driving East looks like in "radio eyes" versus driving North based on relative arrivals of repetitive timing structures within digital broadcasts, etc. So already you can handle short dropouts and freewheel through short GPS dropouts (a few minutes) using the opportunistic radio data with only a few minutes of operation. The further to go and more you have the system on, the better, and eventually you work out where all the transmitters are (short range cellular are located very quickly, long range DAB, DVB etc take more time to locate). Eventually you have enough data to confidently state where the transmitter is and it goes in the database. These signals punch into cities much better than GPS, so calibrating these sources on the way in means that you can use them during GPS dropout inside the city. The accuracy depends on a whole host of factors - typically ~10-150 metres, and

So in summary - outdoors we use time-of-arrival and carrier phase measurements, with signal strength being a secondary measurement, whereas indoors signal strength measurements combined with Simultaneous Localisation ad Mapping is key to high accuracy
Ramsey

Kind of cool. This is one way that Cold War era bombers were to guide themselves to targets. It is also one reason why, during the Cold War, the US Government took such an interest in radio broadcasters, with plans in place to "randomly" black out most stations and restrict all remaining transmissions to specific Civil Defense frequencies.

Its been talked about briefly today but the biggest issue is that the system needs an accurate database to work. That means either you have people driving around all the time getting new data OR you are constantly connecting to the internet and exchanging your position data and those around you all the time to a central network.

The other big problem is the huge database you'll have to carry around. We are talking about trillions of data points in the US alone. The only way you get around this have an a